Just to say, it has been suggested I upgrade from 18.2 to 18.3 after getting the nemo/black screen issue ... but I get the same problem with upgrade manager as above, nowhere is 18.3. I upgraded very recently, but I clearly have 18.2.
Desktop: Cinnamon 3.4.3 (Gtk 3.18.9-1ubuntu3.3)
Distro: Linux Mint 18.2 Sonya